November 11, 2008 -- I was struck, several months ago, by a piece in The Times about the effort to create a new interactive map of the New York City sewer system. For nearly a decade, the Bureau of Water and Sewer Operations — a branch of the Department of Environmental Protection — has been scanning its archive of old engineering maps onto what will soon be a digital map of the system.

Most of those old maps are covered with notes about changes and updates to the system, as are the tens of thousands of index cards that also record field data about the grid beneath us. Some of those maps and cards date back a century and a half, and the system they describe — 6,000-plus miles of pipe — is both a study in sober city planning and a miracle of improvisation...